1. Field of the Invention
The present invention relates to an apparatus for recording and/or reproducing information on and/or from an optical record disk comprising an optical head including a semiconductor laser for emitting a laser beam, an objective lens for projecting the laser beam emitted by the semiconductor laser onto the optical information record disk and a photodetecting means for receiving a return laser beam reflected by said optical information record disk to produce information signal and focusing error signal; a disk driving device including a turntable for supporting the optical information record disk and a spindle motor for rotating said turntable together with the optical information record disk; means for driving at said objective lens in a radial direction of the optical information record disk; and a control means for performing a focus control for moving said objective lens and turntable relative to each other for moving a relative position of a focus point of the laser beam with respect to the optical information record disk in a focusing direction which is parallel with an optical axis of said objective lens.
2. Related Art Statement
In Japanese Patent Application Publication No. 1-35415 published on Jul. 25, 1989, there is described a known apparatus for recording and/or reproducing information on and/or from an optical information record disk such as the magneto-optical record disk. In this known apparatus, when the cartridge having an optical disk installed therein is inserted into the apparatus, the cartridge is inserted into a holder of a cartridge loading mechanism and this holder is movably arranged on a driving member, and when the cartridge is fully inserted into the holder, the driving member is moved downward so that the optical disk is placed on a turntable which is coupled with a driving shaft of a spindle motor. In this apparatus, the optical disk can be place on the turntable without moving the spindle motor and turntable up and down, so that the disk driving device may be simple in construction. However, the holder has to be moved not only horizontally, but also vertically, and therefore the mechanism for driving the holder is liable to be complicated and a stable operation could be hardly attained.
In order to avoid the above mentioned drawbacks, there has been proposed another known apparatus described in Japanese Patent Application Laid-open Publication Kokai Hei No. 4-321972 published on Nov. 11, 1992. In this known optical information record disk apparatus, after a cartridge having a magneto-optical record disk installed therein is inserted into the apparatus, a spindle motor for rotating the optical disk is moved upward such that the optical disk is supported by a turntable provided on a driving shaft of the spindle motor. In this known apparatus, it is no more necessary to provide a mechanism for descending the cartridge in the cartridge loading mechanism, and thus its construction becomes simple and small. Further, in this known apparatus, a focus control including focus search and focus servo is performed by moving the spindle motor, turntable and optical disk in a direction parallel with an axis of the spindle motor such that a distance between the objective lens and the information record plane of the optical disk is changed. Therefore, it is no more necessary to provide, in the optical head, an objective lens driving mechanism for moving the objective lens in a direction of its optical axis and thus the optical head can be made small in size and light in weight. It should be noted that the focus servo control means a control for adjusting a distance between the objective lens and the optical disk in accordance with a focusing error signal by means of a focus servo mechanism so that the light beam is correctly focused on the optical disk, and the focus search control means a control for setting said distance within a controllable range of the focus servo mechanism.
In this known apparatus, the spindle motor is secured to an up-down block, and turntable and cartridge positioning member are secured to the up-down block. When the up-down block is moved upward, a lower surface of the cartridge is supported by projections of the cartridge positioning member and an optical disk installed within the cartridge is supported on the turntable. The disk is firmly secured onto the turntable by means of a permanent magnet. The up-down block is moved up and down by a cum mechanism including a cum gear and a up-down motor for rotating the cum gear by means of a gear box, a cum surface of said cum gear being engaged with a roller arranged rotatably on a side surface of the up-down block. A rotation of the cum gear is detected by a rotary encoder, so that a position of the up-down block can be detected by processing an output signal of the rotary encoder.
In this known apparatus, the position of the up-down block is not directly detected, but is presumed from the rotation of the cum gear. By such an indirect detection, the position of the up-down block could not be accurately detected owing to the reason that the gears contain back rush and thus the output signal detected by the rotary encoder could not precisely represent an amount of the actual up-down movement of the up-down block. It should be noted that the focus control including the focus search and focus servo has to be performed in relation to a position of a movable portion including the up-down block, turntable, cartridge positioning member and spindle motor, but in the known apparatus the position of the movable member could not be detected precisely and it is no more possible to perform the focus control precisely.
Further, in the known disk driving device, substantial parts of the device including the up-down is block, spindle motor, turntable and cartridge positioning member are moved up and down, and thus a relatively heavy load is applied to the up-down motor. Therefore, the up-down motor is liable to be large. Moreover, during the focus control, not only the turntable, but also the up-down block and spindle motor are moved up and down, the projections of the cartridge positioning member might vibrate and thus the projections might hit the cartridge to produce annoying noise.